WHEAT:

Where will 'amber waves of grain' grow in a climate-changed world?

Tiffany Stecker, E&E reporter

ClimateWire: Tuesday, March 29, 2011

Giving new meaning to toasted wheat, a team of agricultural researchers has spent the past three years and almost a million dollars installing electric heaters over wheat fields in the desert of Maricopa, Ariz.

Called the "Hot Serial Cereal" project, the experiment is not a move to tempt breakfast-eaters in the morning, but rather to simulate a temperature rise of 2 to 6 degrees Fahrenheit -- the predicted global average increase for the next 50 years.

SPECIAL SERIES

The impact of climate change on wheat, the world's most important food, is increasingly worrisome to food security experts. Rising temperatures and more frequent droughts are among the causes of a widening gap between demand and supplies. E&E examines the issue.

While there is a general consensus that tropical regions will be feeling most of the heat from climate change, no one knows exactly how agriculture and food patterns are going to pan out in a greenhouse gas-affected world. So researchers around the globe are setting up experiments in wheat fields to match -- or refute -- theoretical models. Some experiments use heaters, while others spray concentrated carbon dioxide on plants, copying an expected rise in atmospheric CO2.

Bruce Kimball, a now retired researcher, led the team of scientists from the Agricultural Research Service (ARS), the Agriculture Department's arm for scientific research, in Maricopa. A soil scientist by training, Kimball has spent a good portion of his career simulating a 2050 world in agriculture fields. In many of his past experiments, he created high-CO2 environments for plants, from sour oranges to sorghum, in what are known as Free Air Concentration Experiments, or FACE.

The heaters were turned on from December to early January, adding 2 degrees Fahrenheit during the day and 5 to 6 degrees Fahrenheit at night. Wheat was planted every six weeks over two years, a regular cycle from which the "serial" of Hot Serial Cereal comes.

As expected, the heaters accelerated growth, increased soil temperatures, reduced soil moisture, induced mild water stress on the crops and had a nominal effect on photosynthesis. But soil moisture decreased about 13 percent.

"Farmers might laugh at it," said Kimball of the reactions to scientists' seemingly obvious results. For winter wheat planted in September, the heaters allowed it to withstand a substantial frost in December, a time when the plant is usually too young and feeble to bear such cold. Disastrous yield losses were avoided, thanks to the heaters.

"If that was the only experiment you did rate, you'd say, 'Bring on global warming,'" said Kimball, who published the experiment's results in the journal Global Change Biology.

But like any thorough scientist, Kimball and his team did not simply rely on the September-sown wheat to conclude the study. When heat was applied to wheat planted in December, the normal planting period for Arizona, it grew faster, with a growth cycle that was ahead by a week.

Researcher Bruce Kimball. Photo courtesy of the U.S. Department of Agriculture's Agricultural Research Service.

However, this fast growth meant that the grain-filling period was made shorter, and in the end, there were no major improvements in grain yields.

For the crop that was planted in March, yields were much lower than what they should have been, revealing wheat's sensitivity to high temperatures.

"The additional heat just exacerbated the problem" of the summertime temperatures, said Kimball. In Arizona, wheat is typically planted in the fall to avoid summer heat during a critical maturation period. It lies dormant in the winter and develops grain in the spring.

Its growing patterns are very similar to those of California, Mexico and India, which is one of the largest wheat exporters in the world.

There is a narrow latitudinal band that could make rising heat beneficial to growers, Kimball concluded. But farther south, especially in Mexico, the implications of the warming mean serious reductions in crop yields.

FACE-off with computer models

Kimball's experiment, among others, is an example of what is being done to field-test the results of climate models and to see what really happens when you create a warmer world. The conventional wisdom states that while climate change will shrivel crops at the lower latitudes, it will have a beneficial effect higher north. As Kimball saw in his experiment, these conclusions can be true on the micro-scale.

But the overall effects of CO2 remain uncertain, tending to lean toward the negative.

"In 7 out of 10 world regions, the mean impact indicates rising crop yields in 2046-2055 compared to 1996-2005," states a 2010 study prepared for the World Bank by Christoph Müller of the Potsdam Institute for Climate Impact Research, based on 30 different climate scenarios for three different CO2 emission levels.

"However," the study continues, "depending on the climate scenario and the assumptions on effectiveness of CO2 fertilization, all regions may experience significant decreases in crop yields as well as significant increases. The most important factor is the uncertainty in CO2 fertilization, which outweighs the differences in climate scenarios."

Jeffrey White, a researcher with USDA's ARS who worked with Kimball in the wheat fields of Maricopa, agrees. "Probably the biggest controversy is whether the responses to elevated CO2 are represented well enough to allow useful predictions," he said.

These are factors that aren't always taken into account in climate models for agriculture, he added.

"I am currently a modeling skeptic -- I like models but feel that model applications are being pursued at the expense of studies to improve the science within the models," he said.

In an attempt to observe the little-known role of CO2 on plants, unanswered by climate models, scientists are setting up FACE experiments around the world, including in fields in Illinois and Japan. In these experiments, crops are surrounded by structures that blow concentrated levels of CO2 and ozone (another greenhouse gas expected to rise with climate change) and track how they respond.

"One of the main reasons for doing the work here is to provide what's called a validation data set to validate the crop models," said Glenn Fitzgerald, senior research scientist with the Department of Primary Industries in the state of Victoria, Australia. "As long as models are validating what we're seeing, we can see it as a predictive tool."

Fitzgerald oversees one of the largest FACE projects on wheat in Horsham, a town of 20,000 in southeastern Australia with an average rainfall of 400 millimeters per year -- about double the amount in Maricopa. His experiments include 12-meter (39.3-foot) rings encircling the crops with up to 1 ton of carbon dioxide per day. This increases ambient CO2 to about 550 parts per million, and irrigation is increased up to 5.9 inches above non-irrigated levels.

Bruce Kimball adjusts a wind sensor he uses to control the release of carbon dioxide over test wheat plots. Photo courtesy of U.S. Agricultural Research Service.

Plants breathe in CO2 in the process of photosynthesis -- the method of converting sunlight into energy -- that allows them to absorb carbon from the atmosphere. Wheat is especially efficient at taking in carbon, using the excess to build more biomass.

In some of the Horsham FACE results, the CO2 resulted in yield increases of up to 23 percent.

At another, more arid, site in Walpeup, Australia, the percentage of yield growth was even higher -- about 50 percent. Fitzgerald attributes this to an increase in water efficiency of the plant. The stomata, or pores of the leaves of the plant, remained closed for longer under higher carbon conditions and retained more water.

So an increase in CO2 must be good for wheat, right? "Well, that's the simple answer," said Fitzgerald. Like in Kimball's experiments, his results on a micro-scale are optimistic, but "if you also include what we consider in temperature and lower rainfall, the benefits start to disappear."

For example, Walpeup's yields increased as a percentage of its yields acquired under normal CO2 conditions. However, the fact that the town receives 100 millimeters less water (3.94 inches) annually than Horsham means total output is still only half that of its neighbor, located a mere 125 miles to the south.

Australian wheat fields are not irrigated, said Fitzgerald, so rainfall is the only way the crop gets its water.

Increased carbon dioxide does increase total mass, but it tends to do so equally through the leaves, stems and grain. To increase the grain output, breeding and engineering technology is needed to concentrate energy into grain yield, said White, a view most believe is the key to solving the conundrum for world agriculture.

Feeding 9 billion will be tough

Just two years ago, it was not unusual to hear scholars tout the possible benefits of climate change in cold countries' agriculture.

But the silver lining of northern production is fading. Once-optimistic modelers are becoming more skeptical, as the agricultural losses in tropical and southern countries are projected to far outweigh the benefits in the north. Running alongside climate change is rampant population growth, projected to rise to 9 billion by 2050.

While both climatic models and field studies remain open to interpretation in how crops will fare, policy analysts like Will Martin, manager of the World Bank's research group on agricultural and rural development, are bracing for the worst. There is a lot of work to do in very little time, he said, and to date, "it's a pretty pessimistic scenario."

Rocky terrain in Canada and northern Europe may make the northern migration of the crop more difficult, said White. "There's just an awful lot of big rocks," he explained, "pockets of soil that are totally unsuitable for modern agriculture."

Diminishing water resources and growing pest problems, two products of increasing temperatures, are not always accounted for in traditional agro-climatic computer models.

For example, Martin points out, the wheat-growing areas of northern India, Australia and the American Midwest are projected to see 20 to 50 percent drops in yields, according to Christoph Müller's study for the World Bank. While some northern regions may see increases up to 100 percent, according to Müller, these areas are much less expansive. In addition, agricultural workers in the developing world are fleeing farms to find jobs in cities, leaving a dearth in human agricultural capital.

The solution, according to both the plant physiologist and the policy expert, is better breeding and engineering technology for higher yields.

If CO2 does hold a promise for more vigorous growth, said White, "we would need to rebalance between the vegetative growth [of stems and leaves] and grain growth." Breeders, both traditional and bioengineer, would need to select for genetic traits that could take advantage of the additional carbon dioxide, while accounting for scarcer water, longer periods of hot weather and variations in climate.

Giant agriculture companies are already preparing to market drought-tolerant corn, with plans to apply the technology to wheat. Gene banks around the world collect millions of wild varieties with the potential to breed heat-tolerant crops.

"The way to produce food is to produce it smarter, with better technology, rather than with more people," said Martin. To stop the flow of farmers from the countryside "would be getting to it the wrong way."

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